1. Field of the Invention
The present invention relates to a recording paper, to which no special coating has been applied (so-called plain paper) and that is suitable for use in both inkjet recording and electrophotographic recording, and to an image recording method using the recording paper.
2. Description of the Related Art
Inkjet recording is characterized in that coloration is easy, noise at the time of recording and energy consumption are low, and manufacturing costs of printers therefor can be kept low. Because of these characteristics, inkjet recording has come to be widely used in recent years, not only in homes but also in offices. Inkjet recording has also come to be increasingly used together with electrophotographic recording apparatus, such as laser printers and copiers.
Recording media such as plain paper, coated paper and glossy paper for inkjet recording, white film, and transparent film are used in inkjet recording. Particularly when inkjet recording is employed in a laser printer or copier in an office or the like, printing is conducted most often on plain paper, which can be generally used in electrophotographic recording apparatus and is easily available at a low cost. Enhancing the recording suitability of plain paper in inkjet recording is therefore extremely important. However, there have been the following problems (1) to (4) when printing is conducted on plain paper in conventional inkjet recording.
(1) A phenomenon known as feathering occurs, in which ink flows out along the fibers of the paper. Such feathering significantly impairs black letter image quality in particular.
(2) Plain paper is generally treated with a size (water-repelling agent). For this reason, ink absorption is retarded and bleeding occurs between colors at regions where mutually different colors meet.
(3) It is difficult for coloring material to remain on the surface of the paper, and color-forming performance is not sufficient.
(4) Since water-soluble coloring material is used, water resistance of recorded images is insufficient.
In order to alleviate these problems, Japanese Patent Application Laid-Open (JP-A) No. 7-257017 discloses a method in which, using an ink that includes a water-soluble dye, recording is done on a paper including a substance having an ionicity opposite to that of the water-soluble dye in the ink. According to this method, it is possible to obtain ink fixability, sufficient image density, and images having excellent color reproducibility without bleeding when color images are recorded. Moreover, images have excellent water resistance are obtainable.
However, in this method, surface and volume electric resistivity of the paper drop when ionic chemicals are added in order to obtain sufficient image density. As a result, there are instances where toner transfer is poor and image quality worthy of practical use cannot be obtained in electrophotographic recording, whereby the paper cannot be used as a common paper. Meanwhile, although defective transfer does not occur if the amount of the ionic chemical substance added is reduced, the reduction impairs image quality such as print density and color formability at the time of inkjet printing.
In order to alleviate this problem, JP-A No. 2000-85239 proposes a plain paper that can be used in both inkjet recording and electrophotographic recording by adhering a cationic resin (cationic equivalent: 3 to 8 meq/g) in an amount of 0.5 to 2.0 g/sm to set surface electric resistivity to 1.0xc3x97109 to 9.9xc3x971013 xcexa9. However, when a chemical is coated on the plain paper using an ordinary size-press method, as described in the examples thereof, volume electric resistance concomitantly decreases even if the surface electric resistance is in the above-mentioned range. For this reason, defective transfer occurs in electrostatic recording (electrophotographic recording). Moreover, when the coating amount of the cationic resin is close to the lower limit, so that defective transfer does not occur, satisfactory inkjet image quality cannot be obtained in terms of color formation, print density, and the like. JP-A No. 6-219038 proposes a recording paper having a surface pH of 6.5 to 7.8 and surface electric resistance of 1.0xc3x97109 to 1.0xc3x971011 xcexa9, but the same problems occur.
Japanese Patent No. 2943927 proposes a plain paper having a volume specific resistance of 1.0xc3x971011 xcexa9xc2x7cm or less at 20xc2x0 C. and 65% relative humidity. However, this plain paper is proposed from the viewpoint of paper conveyability, and when the volume specific resistance is less than 1.0xc3x97109 xcexa9xc2x7cm, defective toner transfer occurs. In addition, satisfactory inkjet image quality and water resistance cannot be obtained because the paper is not coated with a cationic resin.
It is a task of the present invention to solve the aforementioned conventional problems and to achieve the following object. Namely, it is an object of the invention to provide a recording paper that can be used in both inkjet recording and electrophotographic recording so that, when the paper is printed by inkjet recording, optical density and color formability are high, there is little feathering and bleeding between colors, and images have excellent water resistance, and when the paper is printed by electrophotographic recording using such apparatus as laser printers and copiers, defective toner transfer does not occur and clear images can be obtained. It is also an object of the invention to provide an image recording method using this recording paper.
As a result of extensive research in regard to this task, the present inventors found that penetration into a base paper by a coating solution that contains a cationic resin and is applied to the surface of the base paper is a factor far more important than the mere amount of the solution coated on the surface. That is, the inventors found that distributing the cationic resin in the vicinity of a surface layer of the base paper by minimizing penetration of the coating solution into the base paper when the cationic resin is applied to the surface is effective both for improving image quality in inkjet recording and for securing toner transferability in electrophotographic recording. The inventors came to focus their attention on surface electric resistivity and volume electric resistivity at 22xc2x0 C. and 55% relative humidity as an indicator to measure the penetration of the coating solution containing the cationic resin (i.e., the distribution of the cationic resin in the vicinity of the surface layer). The inventors also came to focus their attention on a corrected Stxc3x6ckigt degree of sizing in order to alleviate feathering and bleeding between colors.
According to a first aspect of the invention, there is provided a recording paper comprising a base paper that is composed mainly of pulp fibers, contains a filler, and is coated with a cationic resin on one or both sides, wherein surface electric resistivity at 22xc2x0 C. and 55% relative humidity is 1.0xc3x97109 to 1.0xc3x971011 xcexa9 and volume electric resistivity at 22xc2x0 C. and 55% relative humidity is 1.0xc3x971010 to 1.0xc3x971012 xcexa9xc2x7cm, with a corrected Stxc3x6ckigt degree of sizing being no less than 10 seconds and no more than 40 seconds.
According to a second aspect of the invention, there is provided a recording paper whose smoothness is no less than 40 seconds and no more than 100 seconds, and whose texture index is no less than 20.
According to a third aspect of the invention, there is provided a method of electrophotographically recording an image, comprising the steps of: uniformly charging a surface of an electrostatic latent image support; exposing the surface of the electrostatic latent image support to light, to thereby form an electrostatic latent image; developing the electrostatic latent image formed on the surface of the electrostatic latent image support, using an electrostatic charge image developing agent, to form a toner image; transferring the toner image onto a recording paper; and fixing the toner image on the recording paper, wherein the recording paper is the recording paper described above.
According to a fourth aspect of the invention, there is provided a method of inkjet recording an image, comprising jetting ink droplets onto a recording paper to record an image on the recording paper, wherein the recording paper is the recording paper described above.